Field of the Invention
Embodiments of the invention relate to a method for producing an anti-blocking hard coat film. Embodiments of the invention more specifically relate to a method for producing a hard coat film which is excellent in anti-blocking properties and transparency and suitable as a member of a touch panel.
Description of the Related Art
In recent years, touch panels have become widespread, which are installed on image display devices, such as a liquid crystal display, a plasma display, and an electroluminescence display and allow input by touching with a finger, a pen, or the like, while observing a display. A member comprising a film base material, such as triacetyl cellulose or polyethylene terephthalate has been frequently used in a touch panel. It has been widely performed to form an abrasion resistant hard coat on the outermost surface on the touch surface side of the film base material so that scratches and the like caused by fingernails or a pen point during the operation of the touch panel do not occur.
Further, a transparent conductive laminate of a film base material and a transparent conductive film such as a metal oxide thin film of indium tin oxide or the like has been frequently used in the touch panel. It has been widely performed to form a hard coat or laminate a hard coat film on the transparent conductive laminate for the purpose of suppressing precipitation of oligomers from the film base material or the like or adjusting the reflection color or transmission color of the laminate.
In the production steps for forming a hard coat film by forming a hard coat on a film base material, for forming a hard coat on a transparent conductive laminate, and for laminating a transparent conductive laminate and a hard coat film, the laminated film may be stored in the state where it is wound in a roll form. Since the laminated film is left with the surface on the hard coat side and the back surface opposite to the hard coat surface being pressed with each other for a long time during the storage, the hard coat surface and the back surface are often strongly adhered. As a result, when the laminated film is withdrawn from a film roll, it cannot be smoothly withdrawn, or the hard coat of the laminated film may be broken.
As a technique of solving such disadvantage, a technique of incorporating fine particles into a coating material for forming a hard coat to provide unevenness on the hard coat surface to reduce the true contact area between the hard coat surface and the back surface is frequently used. However, in order to obtain sufficient anti-blocking properties, it is necessary to use particles having a relatively large size or use a large amount of fine particles, resulting in unsatisfactory transparency for a touch panel.
Thus, there have been proposed techniques of forming a coating film made of a coating material containing inorganic fine particles such as silica on the back surface opposite to the surface on the hard coat side of a film base material to provide unevenness on the back surface (for example, see JP 2011-039978 A and JP 2012-027401 A). However, in order to obtain sufficient anti-blocking properties, these techniques are required to incorporate particles having a relatively large size or to incorporate a large amount of fine particles into the coating material used for the anti-blocking coat. Even when such a coating film is formed on the back surface, there is a disadvantage that the transparency will be unsatisfactory for a touch panel. Further, since inorganic fine particles such as silica have high hardness, there is a disadvantage of the wear of a production apparatus. Further, since highly dispersed inorganic fine particles such as silica have high surface activity and strong adhesion force to metal, there will also be a disadvantage of requiring much labor in the operation of cleaning a coating roller or the like when a coating material containing inorganic fine particles such as silica adheres to the coating roller or the like.
Further, there has been proposed a technique of providing unevenness on the hard coat surface by phase separating the base resin of a coating material forming a hard coat (for example, see JP 2010-163535 A). However, since the effect of the technique is largely influenced by drying, temperature conditions, and the like during production, there is also a disadvantage that it is difficult to industrially stably produce such a hard coat film.
Further, there has been also proposed a technique of gathering an anti-blocking agent on the surface of a hard coat layer (for example, see JP 2010-241937 A). According to this technique, since sufficient anti-blocking properties can be obtained when a small amount of fine particles are used as an anti-blocking agent, transparency sufficient for displays can be secured. However, the technique of JP 2010-241937A is a technique in which “fine particles having a fluorine compound on the surface is used as an anti-blocking agent thereby bleeding the fine particles to the surface of a hard coat layer to effectively form surface unevenness with a small amount of fine particles and impart blocking resistance without reducing the physical properties and transparency of the hard coat layer”. Therefore, this technique cannot be used for the purpose of suppressing precipitation of oligomers from a film base material or the like. Further, even when a conductive film such as an indium tin oxide thin film is intended to be laminated on the anti-blocking hard coat surface, it will be difficult to laminate the film with sufficient adhesion strength. Further, this film is not satisfactory in terms of stain resistance and fingerprint resistance as a film for touch panels operated by touching with a finger or the like.